@misc{SteteKoopmanBargheer2018, author = {Stete, Felix and Koopman, Wouter-Willem Adriaan and Bargheer, Matias}, title = {Signatures of strong coupling on nanoparticles}, series = {Quantum Nano-Photonics}, journal = {Quantum Nano-Photonics}, publisher = {Springer}, address = {Dordrecht}, isbn = {978-94-024-1546-9}, issn = {1871-465X}, doi = {10.1007/978-94-024-1544-5_53}, pages = {445 -- 447}, year = {2018}, abstract = {The electromagnetic coupling of molecular excitations to plasmonic nanoparticles offers a promising method to manipulate the light-matter interaction at the nanoscale. Plasmonic nanoparticles foster exceptionally high coupling strengths, due to their capacity to strongly concentrate the light-field to sub-wavelength mode volumes. A particularly interesting coupling regime occurs, if the coupling increases to a level such that the coupling strength surpasses all damping rates in the system. In this so-called strong-coupling regime hybrid light-matter states emerge, which can no more be divided into separate light and matter components. These hybrids unite the features of the original components and possess new resonances whose positions are separated by the Rabi splitting energy h Omega. Detuning the resonance of one of the components leads to an anticrossing of the two arising branches of the new resonances omega(+) and omega(-) with a minimal separation of Omega = omega(+) - omega(-).}, language = {en} } @misc{SteteSchossauKoopmanetal.2018, author = {Stete, Felix and Schossau, Phillip Gerald and Koopman, Wouter-Willem Adriaan and Bargheer, Matias}, title = {Size Dependence of the Coupling Strength in Plasmon-Exciton Nanoparticles}, series = {Quantum Nano-Photonics}, journal = {Quantum Nano-Photonics}, publisher = {Springer}, address = {Dordrecht}, isbn = {978-94-024-1546-9}, issn = {1871-465X}, doi = {10.1007/978-94-024-1544-5_26}, pages = {381 -- 383}, year = {2018}, abstract = {The coupling between molecular excitations and nanoparticles leads to promising applications. It is for example used to enhance the optical cross-section of molecules in surface enhanced Raman scattering, Purcell enhancement or plasmon enhanced dye lasers. In a coupled system new resonances emerge resulting from the original plasmon (ωpl) and exciton (ωex) resonances as ω±=12(ωpl+ωex)±14(ωpl-ωex)2+g2---------------√, (1) where g is the coupling parameter. Hence, the new resonances show a separation of Δ = ω+ - ω- from which the coupling strength can be deduced from the minimum distance between the two resonances, Ω = Δ(ω+ = ω-).}, language = {en} } @article{SteteSchossauBargheeretal.2018, author = {Stete, Felix and Schossau, Phillip and Bargheer, Matias and Koopman, Wouter-Willem Adriaan}, title = {Size-Dependent coupling of Hybrid Core-Shell Nanorods}, series = {The journal of physical chemistry : C, Nanomaterials and interfaces}, volume = {122}, journal = {The journal of physical chemistry : C, Nanomaterials and interfaces}, number = {31}, publisher = {American Chemical Society}, address = {Washington}, issn = {1932-7447}, doi = {10.1021/acs.jpcc.8b04204}, pages = {17976 -- 17982}, year = {2018}, abstract = {Owing to their ability of concentrating electromagnetic fields to subwavelength mode volumes, plasmonic nanoparticles foster extremely high light-matter coupling strengths reaching far into the strong-coupling regime of light matter interaction. In this article, we present an experimental investigation on the dependence of coupling strength on the geometrical size of the nanoparticle. The coupling strength for differently sized hybrid plasmon-core exciton-shell nanorods was extracted from the typical resonance anticrossing of these systems, obtained by controlled modification of the environment permittivity using layer-by-layer deposition of polyelectrolytes. The observed size dependence of the coupling strength can be explained by a simple model approximating the electromagnetic mode volume by the geometrical volume of the particle. On the basis of this model, the coupling strength for particles of arbitrary size can be predicted, including the particle size necessary to support single-emitter strong coupling.}, language = {en} } @article{SarhanKoopmanPudelletal.2019, author = {Sarhan, Radwan Mohamed and Koopman, Wouter-Willem Adriaan and Pudell, Jan-Etienne and Stete, Felix and R{\"o}ssle, Matthias and Herzog, Marc and Schmitt, Clemens Nikolaus Zeno and Liebig, Ferenc and Koetz, Joachim and Bargheer, Matias}, title = {Scaling up nanoplasmon catalysis}, series = {The journal of physical chemistry : C, Nanomaterials and interfaces}, volume = {123}, journal = {The journal of physical chemistry : C, Nanomaterials and interfaces}, number = {14}, publisher = {American Chemical Society}, address = {Washington}, issn = {1932-7447}, doi = {10.1021/acs.jpcc.8b12574}, pages = {9352 -- 9357}, year = {2019}, abstract = {Nanoscale heating by optical excitation of plasmonic nanoparticles offers a new perspective of controlling chemical reactions, where heat is not spatially uniform as in conventional macroscopic heating but strong temperature gradients exist around microscopic hot spots. In nanoplasmonics, metal particles act as a nanosource of light, heat, and energetic electrons driven by resonant excitation of their localized surface plasmon resonance. As an example of the coupling reaction of 4-nitrothiophenol into 4,4′-dimercaptoazobenzene, we show that besides the nanoscopic heat distribution at hot spots, the microscopic distribution of heat dictated by the spot size of the light focus also plays a crucial role in the design of plasmonic nanoreactors. Small sizes of laser spots enable high intensities to drive plasmon-assisted catalysis. This facilitates the observation of such reactions by surface-enhanced Raman scattering, but it challenges attempts to scale nanoplasmonic chemistry up to large areas, where the excess heat must be dissipated by one-dimensional heat transport.}, language = {en} } @phdthesis{Stete2020, author = {Stete, Felix}, title = {Gold at the nanoscale}, doi = {10.25932/publishup-49605}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-496055}, school = {Universit{\"a}t Potsdam}, pages = {X, 186}, year = {2020}, abstract = {In this cumulative dissertation, I want to present my contributions to the field of plasmonic nanoparticle science. Plasmonic nanoparticles are characterised by resonances of the free electron gas around the spectral range of visible light. In recent years, they have evolved as promising components for light based nanocircuits, light harvesting, nanosensors, cancer therapies, and many more. This work exhibits the articles I authored or co-authored in my time as PhD student at the University of Potsdam. The main focus lies on the coupling between localised plasmons and excitons in organic dyes. Plasmon-exciton coupling brings light-matter coupling to the nanoscale. This size reduction is accompanied by strong enhancements of the light field which can, among others, be utilised to enhance the spectroscopic footprint of molecules down to single molecule detection, improve the efficiency of solar cells, or establish lasing on the nanoscale. When the coupling exceeds all decay channels, the system enters the strong coupling regime. In this case, hybrid light-matter modes emerge utilisable as optical switches, in quantum networks, or as thresholdless lasers. The present work investigates plasmon-exciton coupling in gold-dye core-shell geometries and contains both fundamental insights and technical novelties. It presents a technique which reveals the anticrossing in coupled systems without manipulating the particles themselves. The method is used to investigate the relation between coupling strength and particle size. Additionally, the work demonstrates that pure extinction measurements can be insufficient when trying to assess the coupling regime. Moreover, the fundamental quantum electrodynamic effect of vacuum induced saturation is introduced. This effect causes the vacuum fluctuations to diminish the polarisability of molecules and has not yet been considered in the plasmonic context. The work additionally discusses the reaction of gold nanoparticles to optical heating. Such knowledge is of great importance for all potential optical applications utilising plasmonic nanoparticles since optical excitation always generates heat. This heat can induce a change in the optical properties, but also mechanical changes up to melting can occur. Here, the change of spectra in coupled plasmon-exciton particles is discussed and explained with a precise model. Moreover, the work discusses the behaviour of gold nanotriangles exposed to optical heating. In a pump-probe measurement, X-ray probe pulses directly monitored the particles' breathing modes. In another experiment, the triangles were exposed to cw laser radiation with varying intensities and illumination areas. X-ray diffraction directly measured the particles' temperature. Particle melting was investigated with surface enhanced Raman spectroscopy and SEM imaging demonstrating that larger illumination areas can cause melting at lower intensities. An elaborate methodological and theoretical introduction precedes the articles. This way, also readers without specialist's knowledge get a concise and detailed overview of the theory and methods used in the articles. I introduce localised plasmons in metal nanoparticles of different shapes. For this work, the plasmons were mostly coupled to excitons in J-aggregates. Therefore, I discuss these aggregates of organic dyes with sharp and intense resonances and establish an understanding of the coupling between the two systems. For ab initio simulations of the coupled systems, models for the systems' permittivites are presented, too. Moreover, the route to the sample fabrication - the dye coating of gold nanoparticles, their subsequent deposition on substrates, and the covering with polyelectrolytes - is presented together with the measurement methods that were used for the articles.}, language = {en} }